HANOI, Vietnam - Vietnam said Thursday it did not know the whereabouts of three Chinese dissidents said by their families to have disappeared while traveling along Vietnam's border with China.

Foreign Ministry spokeswoman Phan Thuy Thanh said an investigation found that the three arrived in Vietnam on June 16 and visited Hanoi and the northern province of Quang Ninh, which borders China.

They left Quang Ninh on June 26 and "since then they have not registered at any hotel in Vietnam," she said.

Thanh denied reports that Vietnam had arrested the three, or that their bodies had been found near the Chinese border.

Two of the missing dissidents — Wang Bingzhang and Zhang Qi — are U.S. permanent residents, while the third, Yue Wu, lives in France. All three are active in pro-democracy movements.

They have not been in contact with friends or family since June 26, when Wang telephoned a friend who said Wang discussed the possibility of trying to enter China. The two had planned to call each other again June 29.

A U.S-based activist group, China Democracy Party, has accused Chinese authorities of kidnapping the three.

Wang Xizhe, co-chair of the China Democracy Party, said they had arrived in Hanoi on June 16 to meet secretly with Chinese labor leaders and were abducted by Chinese security forces on June 26. They are being held at an undisclosed location, he said.

The Chinese Foreign Ministry ( news - web sites) has denied knowledge of the case.

The China Democracy Party said Wang Bingzhang, 54, was jailed twice in China for speaking out against the communist government.

He went into exile in Canada in 1979 and has lived in New York since the 1980s, publishing a pro-democracy magazine and organizing the Chinese Alliance for Democracy. He slipped into China in 1998 but was caught and deported.

Yue, 54, was a labor leader in the 1989 pro-democracy protests in Beijing's Tiananmen Square, the China Democracy Party said.

Zhang, a leader of banned health and meditation sect Zhong Gong, fled to Thailand in 2000 to escape government persecution. She was given political asylum in the United States last year.

Thanh said Vietnamese authorities were still investigating the case.

Thu Aug 15, 6:20 AM ET